The present invention is broadly concerned with apparatuses for raising and supporting a shallow footing or foundation that has settled due to inadequate compaction of soil and other fill material due to erosion, soil consolidation, dehydration, or other causes. Various piering systems are currently in use for this purpose, and utilize piers of varying configuration and materials including wood, concrete, reinforced concrete, steel pipe, and steel bar stock. A pier is installed underneath or adjacent to a failed footing, and then the load of the footing is transferred to the installed pier by a bracket or load transfer device that is attached to the footing.
This invention deals specifically with a method and apparatus to be used for the installation of pipe piers. In the current art, a pipe pier is advanced into the ground using hydraulic driving cylinders, such as jacks, until a predetermined resistance against the pier is met. The pier is then terminated at an elevation that will allow a foundation load to be transferred to it via a bracket or load transfer mechanism connected to the foundation.
Pipe pier installation apparatuses utilize either single or dual cylinder assemblies are typically used, whereby pier sections are added, section by section, as the pier is advanced into the ground. The depth to which a pier can be advanced is dictated by soil conditions, the driving force of the hydraulic cylinder(s), and the overall strength of the installation assembly.
Single cylinder installation assemblies push piers into the ground, with the piston rod pushing directly on top of the pier, while dual cylinder assemblies are typically inverted, utilizing a reaction to their driving force to pull the pier. One drawback of the single cylinder system is driving force. To develop enough driving force to push piers through dense soils, a single cylinder will either require a prohibitively large diameter, or an additional strength requirement to accept higher hydraulic pressures. The larger diameter cylinder becomes more awkward to handle in the field, and more prone to leakage. The use of high-pressure cylinders increases weight, which again makes the apparatus more cumbersome in the field, and requires larger and costlier hydraulic motors. Another shortfall of the single cylinder, push pier apparatuses currently in use is that they limit the length of pier sections that can be driven. For a single cylinder to be used in driving a pier, it must be concentrically positioned above the pier. This limits pier section lengths to the height inside the apparatus less the space taken up by the mounted cylinder, which impedes installation by requiring the constant insertion and removal of spacers.
Dual cylinder assemblies are more frequently used, as they resolve many of the problems attendant with single cylinder systems. The dual cylinders straddle the pier sections, and thus the pier sections are not limited in length by the available distance above the top of the pier within the installation assembly. Present art pertaining to dual cylinder assemblies often utilizes inverted cylinders that pull the pier into the ground as piston rods are retracted into the cylinders. In this arrangement, the pressurized cylinder chambers used in driving the pier contain the piston rods. As hydraulic fluid is pumped into the cylinders, it cannot act against the entire surface area of the pistons, as some of the available area is taken up by the piston rods. The chambers absent of the piston rods are pressurized during the backstroke, to position the apparatus for the next advancement. The cylinders are therefore not being used in their most effective manner when inverted.
Direct drive power cylinders are employed in the prior art whereby their full hydraulic capacity is used when driving piers. While this is the most efficient manner for driving piers, the assembly hardware for installing the power cylinders can be extremely heavy and unwieldy in the field. The efficiency of workers who must install the apparatus to the piers and supported foundation must be taken into consideration; a lighter power cylinder assembly would lead to faster installations, while causing less fatigue and injuries to the worker. It would be advantageous to have an apparatus for easily and quickly mounting a power cylinder to an assembly for driving a pier into the ground adjacent a footing to be supported.